Taut band suspension system

ABSTRACT

A taut band suspension system for an electrical measuring instrument including a taut band, an inner band anchor connected to an armature assembly and an outer band anchor connected to a frame member. The taut band is &#39;&#39;&#39;&#39;welded&#39;&#39;&#39;&#39; to tab portions formed integrally on each band anchor and located along the axis of rotation of the armature assembly. The taut band is thus welded along a portion of its length and directly along the axis of rotation of the armature assembly which it rotatably supports.

United States Patent [72] Inventors JohnRKain FOREIGN PATENTS MM M4 m an m w m m M a m mm B mm Uh u" p m m mm w 0 mm r .HBSWWM m m w a m U3 h Ah m mm 73 .w 55 L. 99 w R H h m m m 0 1 a G 96 S! 0 um m 0 fi nm 1 PA M w n mu a m um y an m m mm c u gum Mn mw v ,1 m m mmo l u MCWMMAG a N m NdmM ee p afi AFPA flflfl 2247 [[[l 541 TAUT BAND SUSPENSION SYSTEM 9 Claims, 8 Drawing Figs.

ABSTRACT: A taut band suspension system for an electrical measuring instrument including a taut band, an inner band anchor connected to an armature assembly and an outer band anchor connected to a frame member. The taut band is welded" to tab portions formed integrally on each band anchor and located along the axis of rotation of the armature as- R 1 4M U m IHMM M 36 l [511 m. so

References Cited UNITED STATES PATENTS 3,325,734 6/1967 Peltola sembly. The taut band is thus welded along a portion of its length and directly along the axis of rotation of the armature assembly which it rotatably supports.

PATENTEDMJB sun SHEET 1 OF 2 FIG] FIGZ INVENTOR JOHN F. KAlN WILUAM JI-SCHULTZ CARL F. VZN BENNEKOM ATTORNEY new Ll PATENIED AUG 3 an SHEET 2 [IF 2 INVENTOR JOHN F. KAlN WILLIAM J SCHULTZ I CARL F. VN BENNEKOM BY X/Zfi ATTORNEY TAUT BAND SUSPENSION SYSTEM BACKGROUND OF THE INVENTION generally connected to the movable armature assembly to yield a readout with respect to a faceplate or scale mounted behind the pointer as the torque is a function of the current magnitude.

In the past, the movable armature assembly in D Arsonval movement instruments has been supported by a rigid shaft having pivots which are rotatable in jewel bearings. Such support systems, commonly known as pivot-and-jewel systems,

present substantial friction which increases with use and generates random errors due to axial and radial errors within the bearings.

Recently, taut band suspension systems have come into widespread use because they overcome the problem of bearing friction and wear. Taut band suspension systems are characterized by the suspension of the armature assembly on two extremely fine metal bands which are held in tension by resilient anchors supported on an instrument frame. Current is conducted to a coil on the armature assembly by the taut bands causing the the coil and instrument pointer to rotate through an angle related to the magnitude current in the coil. Countertorque is produced by the twisting action on the bands. This countertorque performs the function of coil springs in the pivot-and-jewel suspension systems to return the instrument pointer to its zero point.

Diverse arrangements for attaching taut bands to the armature assembly and frame have been evolved. The more wide] used arrangements can be grouped into three categories:

l. Soldering the bands;

2. Clamping the bands between jaws; and

3. Connecting the bands to violin-type crosspiece attachments.

Soldering the bands does provide firmcontact between the bands and points of attachment which guarantees a uniform current transfer. Soldering the bands, however, demandsa great deal of skill, especially when used for extremely thin bands as poorly soldered bands result in almost immediate destruction of the suspension system.

Clamping the band between two jaws creates good electrical contact, but it also creates additional pressure on the band. Local stress peaks may also be created in connection with the abrupt change of cross section associated with this arrangement. The jaws thus have to be well rounded at the clamping area to eliminate this problem. Additionally, from a manufacturing standpoint, clamping is a tedious and time-consuming job.

Connecting the band to a violin-crosspiece attachment is the most widely used arrangement. However, it also generates the greatest number of problems. In this arrangement the taut band is generally led through a notch or groove in a rounded bridge crosspiece. Welding or soldering is done beyond the rounded bridge and results in a significant amount of wasted band material. In addition, this arrangement generally demands an anchor-to-band subassembly because it is not possible to work at the armature assembly adjacent the inncr band anchor. The existence of this subassembly, especially with two fragile bands, constitutes a serious obstacle to automating the instrument assembly. The location of the effective band end, defined where the taut band just contacts the anchor, is ex tremely critical. Its location depends on a number of factors including the band placement with respect to the notch or groove and the final position of the band anchor. Such positioning is susceptible to movement after calibration of the instrument; and such movement can destroy the instrument balance and accuracy. Further, the band is rectangular in cross section and may tend to bow slightly from the axis of rotation of the armature assembly when bent about the crosspiece.

It is an object of this invention, therefore, to provide a taut band suspension system which substantially eliminates the above-mentioned problems associated with prior suspension systems.

It is another 'object of this invention to provide a suspension system in which a band is welded directly along the axis of rotation of the armature member which it rotatably supports.

It is a further object of this invention to provide a suspension system which yields the advantages of a clamping system but which is less expensive to implement and more readily adapted for automation.

SUMMARY Briefly stated, the objects of this invention are carried out by providing a suspension system which comprises a piece of taut band material welded to the inner and outer band anchors along the axis of rotation of the armature assembly.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the .invention, an understanding of the above and further objects of the advantages of this invention may be gained from the following detailed description of a preferred embodiment in connection with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS I DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT In the FIGURES like numerals refer to like elements throughout. One' example of an electrical indicating mechanism, generally designated by numeral 10, which utilizesa suspension system incorporating this invention, is shown in FIGS. 1 and 2 prior to being placed within an instrument casing. The instrument mechanism 10 comprises basically a frame assembly 12, a magnet assembly 14 and armature as sembly 16.

The frame assembly 12 includes a support member 18 and a combination flux cup and shield 20. A top portion 19 and a bottom portion 21 of the support member 18 are connected together by a leg portion. Openings 22 in the top portion 19 permit attachment of the support member, and thus the instrument mechanism 10, to the instrument casing. The support member 18 fits within and is engaged and restrained by the flux cup and shield 20.

The magnet assembly 14 includes a cylindrical, compressed Alnico permanent magnet 24 and arcuate pole pieces 26 which are rigidly attached to the outer perimeter of the permanent magnet 24 as best shown in FIG. I. The pole pieces 26 may be formed of any suitable magnetic material such as steel. Other magnetic pole piece configurations are adapted for use in instruments utilizing this invention. Notwithstanding the configuration of the magnetic assembly 14, it is important that the pole pieces 26 and the adjacent portions of the flux cup and shield 20 define a uniform air gap therebetween.

The armature assembly 16 comprises a coil support member 28 and a wound copper coil 30. The coil support member 28, which is generally rectangularly shaped with a U-shaped cross section, is formed to rotate freely in the air gap between the magnet assembly 14 and the flux cup and shield 20, as best shown in FIG. 2. Free rotation is possible when the armature assembly 16 is supported for rotation about an axis AA by the suspension system to be described in detail. An indicating pointer 32 is rigidly coupled to the coil support member 28 for rotation therewith.

In operation, current in the copper coil 30 produces a magnetic field which interacts with the magnetic field generated by the permanent magnet 24 to rotate the armature assembly 16 with respect to the permanent magnet 24. The angular displacement of the armature assembly 16 and the indicating pointer 32 with respect to an instrument faceplate located behind the pointer is directly related to the current magnitude.

One function of any taut band suspension system is supporting the armature assembly 16 for rotation about the permanent magnet 24. Other functions of the taut band include electrically connecting the coil 30 to electrical input terminals and providing restoring torque to the armature assembly 16. As shown in detail in FIGS. 3 and 4, the taut band suspension generally comprises an inner band anchor 40, a resilient outer band anchor 42 and a taut band connected between the inner band anchor 40 and the outer band anchor 42 which is generally rectangular in cross section.

One of the inner band anchors 40 is constructed of a rectangular, electrically conductive plated member approximately the same width as the coil support member 28. The inner band anchor 40 lies upon and is supported by upstanding leg portions 45 (FIG. 4) of the U-shaped support member 28. It is rigidly connected to the coil support member 28 by crimping over a plurality of integral tabs 46 on the support member 28 as shown in FIG. 3.

As best shown in FIG. 4, a plurality of integrally formed arms 48, 50 and 52 extend from the inner band anchor 40. One end of the copper coil 30 is electrically connected to the arm 48. The arm 50, which extends from one end of the anchor 40 and includes a pair of rightangle bends and terminates with a portion 54, supports the indicating pointer 32 after final assembly. The plurality of arms 52 balance the finally assembled moving portions of the instrument mechanism. Balance weights can be added to the arms 52 as necessary.

An integral tab 58, located near the center of the flat plate portion of the inner band anchor 40, serves a dual purpose. The primary function of the tab 58 is to anchor one end of the taut band 44 as described hereinafter. Its secondary function is to provide a shock stop by limiting the radial displacement of the armature assembly 16. This stopping action occurs when the tab 58, normally free within a snap-in bushing 60 is located in an opening 62 within the support member 18 is driven by shock to engage a bushing wall 64.

A resilient outer band anchor 42, which is of generally U- shaped configuration as best shown in FIGS. 3 and 4, comprises a first leg portion 66, a curved bight portion 68, a second leg portion 70, and a band anchor portion 72 which extends from the free end ofthe leg portion 70. The first leg portion 66 includes a circular opening 74 which receives the snap-in bushing 60, the bushing 60 thereby connecting the anchor 42 to the support member 18.

A second member 75 is located between the support member 18 and one outer band anchor 42 and is connected to the support member 18 by means of the snap-in bushing 60. The member 75 provides two functions. It serves as an electrical connection, by means of a tab 76, for one of the lead-in lines to the meter. Secondly, an opening 78 in the member 75 is adapted to receive an arm of a zero reset button. When the zero reset button is rotated, the outer band anchor 42 is displaced thereby altering the taut band orientation. This alteration of the taut band orientation causes the indicated zero point of the instrument to change.

The suspension system located on the opposite end of the instrument mechanism 10 is identical to that described above with the exception that the inner band anchor 40 described above is replaced by an inner band anchor subassembly 80 (FIG. 3) which comprises a small rectangular flap plate with an integral tab portion 82 and an insulating member 84. The inner band anchor subassembly 80 is again connected to the support member 28 by crimping over tabs 46. The insulating member 84 isolates the inner band anchor from the coil support member 28 so that the coil is not short circuited.

The details of affixing the taut band to the band anchors along the axis of armature rotation can now be described. Normally the taut band is initially affixed to the inner band anchor. As specifically shown in FIG. 4, the tab 58 is bent back on itself. As detailed in FIG. 5A, the tab initially comprises a flat portion 86 having a rectangular opening 88 centered on a bending axis 90 and the centerline 92 of the tab 58. The opening 88 is sufficiently wide to permit the taut band to pass therethrough when it is centered on the coil. When the inner band anchor is formed, the tab 58 is bent about the axis 90 to the configuration of FIGS. 4 and 5B. As a result, the free end portion.94 of FIGS. 5A and SB coacts with the base of the tab 58 to clamp the taut band 44 after it is fed through the opening 88 and properly located. Resistance welding or other appropriate techniques can then be used to clamp and bond the taut band to the tab 58 and thereby bond the taut band to the outer band anchor along the axis of armature rotation.

While the term welded is used in this specification to denote how the band and anchors are bonded, it is believed that a true weld does not exist. If the band and anchor were raised to a true welding temperature, the band characteristics and properties would be destroyed or adversely affected. In actual practice, the anchor and band are heated under pressure for a certain time period in a resistance welder. It is believed, however, that the plating on the anchor is merely flowed around the band to form the bond.'l-lowever, for purposes of explanation, the term welded" is used to denote this condition or property.

As shown in FIG. 5B, the tab 58 is formed with radiused surfaces 96 and 98. These surfaces eliminate local stresses which were encountered in the prior art clamping techniques. However, the clamping technique advantages are retained by this configuration of the inner band anchor while the additional problems of manufacture have been greatly simplified.

After the inner band anchor and taut band have been welded, the outer band anchor is deflected until the tab portion lies on the axis of armature rotation. Referring specifically to FIG. 6A, the tab portion 72 is initially extended. A notch 100 is centered on a transverse bending axis 102. The notch depth is controlled so that the taut band can be centered on the axis of armature rotation. After the notch 100 is cut, two clamping sections 106 and 108 are defined. The tab portion 72 is then bent about the axis 102 to the configuration shown in FIGS. 4 and 6B. Radiused portions 110 and 112 also eliminate local stresses. After the taut band 44 is led through the space between the clamping sections 106 and 108, the assembly is clamped and welded. When the outer band anchor is subsequently released, it remains on the axis of armature rotation and places the taut band 44 in tension. Further, in accordance with this invention, the taut band 44 has been bonded to the outer band anchor along the axis armature rotation. The taut band may be cut with a minimum of waste material.

By utilizing a suspension system constructed in accordance with this invention, the taut band material may be handled from a coil while positioning and welding. After welding it can be cut next to the weld with a minimum of band waste. Since bending the band about or beneath any other member is not required, the band material may be drawn straight from a reel thereby avoiding material kinking or breaking. As the band is welded along the axis of armature rotation, any bowing tendencies are substantially eliminated. Therefore, it should be readily apparent from the above description, that a suspension system constructed in accordance with this invention has potential for taut band material savings and for instrument assembly automation.

While a preferred embodiment of this invention has been shown and described. it will be obvious to those skilled in the art that there are certain changes and modifications which may be made in the illustrative embodiment without departing from this invention in its broader aspects. For example, it is felt that modifications to the band anchors such as using separate weld pads to replace integral clamping portions can be incorporated in a taut band instrument without departing from the true spirit and scope of this invention as defined in the appended claims.

What we claim as new and desire to be secured by Letters Patent of the United States is:

1. In an electrical measuring instrumentincluding a frame member, means for providing a magnetic field and an armature assembly, the improvement of means for suspending the armature assembly for rotation about an axis within the magnetic field comprising:

a. a taut band;

b. an inner band anchor including a flat plate connected to the armature assembly having an integral .tab extending perpendicularly therefrom along the axis of rotation, one end of said taut band being bonded to said tab; and

c. an outer band anchor connected to the frame member having an integral tab extending along the axis of rotation, the other end of said taut band being bonded to said tab.

2. An electrical measuring instrument as recited in claim 1 wherein said inner band anchor additionally comprises clamping means welded to said tab and said taut band whereby said taut band is clamped between said tab and said clamping means.

3. An electrical measuring instrument as recited in claim 2 wherein said inner band anchor clamping means comprises an integral extension of said tab having an aperture formed therein, said extension being bent about an axis transverse to said tab and substantially centered on said aperture, said taut band passing through said aperture and being clamped and welded to said tab and said extension.

4. An electrical measuring instrument as recited in claim 3 wherein portions of said tab and extension adjacent said taut band of said aperture are radiused.

5. An electrical measuring instrument as recited in claim -l wherein said outer band anchor comprises a generally U- shaped member including a pair of leg portions and a generally curved connecting bight portion and said integral tab extends from one of said leg portions.

6. An electrical measuring instrument as recited in claim 5 wherein said outer band anchor additionally comprises clamping means bonded to said tab and said taut band whereby said taut band is clamped between said tab and clamping means.

7. An electrical measuring instrument as recited in claim 6 wherein said outer band anchor clamping means comprises an integral extension of said tab having a transversely extending notch formed therein, said extension being bent about an axis transverse to said tab and substantially centered on said notch, said taut band passing through said notch and being clamped and welded to said tab and said integral extension.

8. An electrical measuring instrument as recited in claim 1 additionally comprising a second taut band, a second inner band anchor, a second outer band anchor, and integral tabs on said second inner and outer band anchors aligned on the axis of armature rotation, said integral tabs being bonded to said second taut band at the ends thereof and along the axis of armature rotation, said first and second inner band anchors being connected to opposite sides of the armature assembly and said first and second outer band anchors being connected to the frame member whereby the armature assembly is suspended from the frame member for rotation in the magnetic field. v

9. An electrical measuring instrument as recited in claim 8 wherein said second inner band anchor is insulated from the armature assembly. 

1. In an electrical measuring instrument including a frame member, means for providing a magnetic field and an armature assembly, the improvement of means for suspending the armature assembly for rotation about an axis within the magnetic field comprising: a. a taut band; b. an inner band anchor including a flat plate connected to the armature assembly having an integral tab extending perpendicularly therefrom along the axis of rotation, one end of said taut band being bonded to said tab; and c. an outer band anchor connected to the frame member having an integral tab extending along the axis of rotation, the other end of said taut band being bonded to said tab.
 2. An electrical measuring instrument as recited in claim 1 wherein said inner band anchor additionally comprises clamping means welded to said tab and said taut band whereby said taut band is clamped between said tab and said clamping means.
 3. An electrical measuring instrument as recited in claim 2 wherein said inner band anchor clamping means comprises an integral extension of said tab having an aperture formed therein, said extension being bent about an axis transverse to said tab and substantially centered on said aperture, said taut band passing through said aperture and being clamped and welded to said tab and said extension.
 4. An electrical measuring instrument as recited in claim 3 wherein portions of said tab and extension adjacent said taut band of said aperture are radiused.
 5. An electrical measuring instrument as recited in claim 1 wherein said outer band anchor comprises a generally U-shaped member including a pair of leg portions and a generally curved connecting bight portion and said integral tab extends from one of said leg portions.
 6. An electrical measuring instrument as recited in claim 5 wherein said outer band anchor additionally comprises clamping means bonded to said tab and said taut band whereby said taut band is clamped between said taB and clamping means.
 7. An electrical measuring instrument as recited in claim 6 wherein said outer band anchor clamping means comprises an integral extension of said tab having a transversely extending notch formed therein, said extension being bent about an axis transverse to said tab and substantially centered on said notch, said taut band passing through said notch and being clamped and welded to said tab and said integral extension.
 8. An electrical measuring instrument as recited in claim 1 additionally comprising a second taut band, a second inner band anchor, a second outer band anchor, and integral tabs on said second inner and outer band anchors aligned on the axis of armature rotation, said integral tabs being bonded to said second taut band at the ends thereof and along the axis of armature rotation, said first and second inner band anchors being connected to opposite sides of the armature assembly and said first and second outer band anchors being connected to the frame member whereby the armature assembly is suspended from the frame member for rotation in the magnetic field.
 9. An electrical measuring instrument as recited in claim 8 wherein said second inner band anchor is insulated from the armature assembly. 